Day 10 part 2

2024/src/main/kotlin/day10.kt

@@ -7,6 +7,13 @@ fun main() {
         }
 
     println("Part 1: $part1")
+
+    val part2 = map.findCoordinatesOf(0)
+        .fold(0) { acc, start ->
+            acc + map.pathRating(start)
+        }
+
+    println("Part 2: $part2")
 }
 
 fun <T> Grid<T>.findCoordinatesOf(value: T) = sequence {
@@ -32,4 +39,19 @@ fun Grid<Int>.pathsToTop(coordinate: Grid.Coordinate): Set<Grid.Coordinate> {
         .fold(emptySet()) { acc, next ->
             acc + pathsToTop(next)
         }
+}
+
+fun Grid<Int>.pathRating(coordinate: Grid.Coordinate): Int {
+    val height = get(coordinate)
+
+    if (height == 9) {
+        return 1
+    }
+
+    return Direction.entries
+        .map { coordinate.step(it) }
+        .filter { it in this && this[it] == height + 1 }
+        .fold(0) { acc, next ->
+            acc + pathRating(next)
+        }
 }